WASHINGTON – The United Nations investigation of a deadly attack in Syria is likely to show "overwhelming” evidence of chemical weapons use, U.N. Secretary-General Ban Ki-Moon said Friday.

Ban’s comments suggest that the long-awaited report, which could be released as early as Monday, according to U.N. diplomats, will help the United States and its allies build their case against Syria at the U.N. Security Council, even though the report will not specifically say who was responsible.

The U.S. blames the Aug. 21 attack on the government of Syrian President Bashar Assad and says it killed more than 1,400 people in Damascus suburbs. The Syrian government maintains it was a provocation by rebels intended to persuade the international community to intervene in the 2 1/2-year-old war.

Appearing at a U.N. meeting he apparently thought was off the record, Ban said, “I believe that the report will be an overwhelming, overwhelming report that chemical weapons [were] used, even though I cannot publicly say so at this time, before I receive the report.

The U.S., France and Britain are seeking passage of a Security Council resolution that would threaten military action against Syria if it failed to follow through on a promise to surrender its chemical weapons arsenal to international control. Russia and China, which both have veto power on the council, have resisted the threat of force.

Meanwhile, U.S. Secretary of State John F. Kerry and Russian Foreign Minister Sergei Lavrov, meeting for a second day Friday in Geneva to try to flesh out a plan for the destruction of Syria’s chemical weapons, said they discussed how to move ahead with a long-stalled peace process.

The diplomats said they would meet again after a U.N. General Assembly session in New York in two weeks to try to set a date for a second peace conference in Geneva, to follow up on one held in the Swiss city last year.

The first Geneva conference, in June 2012, produced a tentative transition plan for the Syrian government that has largely come to naught as fighting rages between Assad's forces and rebels seeking to overthrow his government. Attempts to convene a sequel have so far been unsuccessful.